Separation of sodium chromate from the high alkaline media based on precipitation transformation using barium hydroxide
In this paper, a novel precipitation transformation system, namely using barium hydroxide as the separation medium, was adopted to achieve the separation of sodium chromate from the concentrated NaOH solution. The alkaline solution was obtained in the liquid-phase oxidation leaching process of chromite using the so-called “sub-molten salt”. In this separation process, Na2CrO4 was transferred from the liquid phase to solid phase BaCrO4 by Ba(OH)2 precipitation. Subsequently, the effect of parameters such as reaction time, reaction temperature, material ratio, NaOH concentration, and dilution multiple on the separation behavior of sodium chromate was discussed. Then, the macroscopic kinetics of chromium reaction in the separation system was investigated in depth. The results showed that the new separation process was able to reduce obviously the reaction requirements and have a higher separating efficiency. The conversion efficiency of sodium chromate exceeded 92% under the condition of Na2CrO4-to-Ba(OH)2 molar ratio of 1:1, NaOH concentration of 50 wt.%, reaction time of 120 min, no dilution, and reaction temperature of 60 ℃. From the perspective of the macroscopic kinetics, the apparent activation energy of the reaction process Ea=6.87 kJ·mol-1, the apparent rate constant k=A·e-6870/RT, and the pre-exponential factor A=0.06 min-1 were obtained. And the enthalpy of activation and the entropy of activation was calculated by using the Eyring Equation, with and . The results could provide data support and theoretical guidance for the separation of chromate in the high concentration of the alkaline sub-molten salt solution.